Die casting machine

ABSTRACT

A die casting machine capable of reducing the pressure in a die cavity to a lower level such as a substantially perfect vacuum, having a movable die and a fixed die, a vacuum pump for reducing pressure in a cavity formed between the dies, and an injection apparatus for injecting and filling molten metal into the cavity with reduced pressure, at least one of the dies having an evacuation path connected with the vacuum pump and communicated with the cavity, a valve element for opening and shutting the evacuation path, and an electromagnetic driving means for making the valve element move linearly in the opening and shutting direction by electromagnetic force.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a die casting machine using vacuum diecasting, that is, die casting in a state with pressure in the cavityreduced.

2. Description of the Related Art

A die casting machine is provided with a pair of dies, a fixed die plateand a movable die plate for holding these dies, a clamping apparatus forclamping the dies, an injection apparatus for injecting molten metalinto a cavity formed between the dies, a molten metal supplyingapparatus for supplying the molten metal to the injection apparatus, andso on. In such a die casting machine, a die casting is obtained byclamping the dies, supplying molten metal into a sleeve of the injectionapparatus, injecting the molten metal into the cavity, and filling thecavity with the molten metal.

One of the causes of uneven quality of die castings is the inclusion ofgas in the die castings. That is, molten metal injected into the cavityand filled in the cavity at a high speed and under a high pressure formsa turbulent flow in the sleeve and the cavity. Due to this, gas such asair or vaporized parting agent is mixed into the molten metal.

In order to overcome the above problem, there is known the vacuumcasting method for decreasing the inclusion of gas and reducingunevenness of die castings caused by the inclusion.

In a die casting machine using the vacuum casting method, as disclosedfor example in U.S. Pat. No. 2,785,448, the inclusion of gas into themolten metal is suppressed by injecting the molten metal into the cavityand filling the cavity with the molten metal in a state with thepressure reduced by a vacuum pump.

In the above die casting machine using vacuum casting, in order to casta product with a high strength and high quality, it is required to beable to create a higher vacuum in the cavity and maintain the vacuumstate.

If the cavity is not made a high vacuum, it is difficult to obtainenough of an effect by the vacuum die casting, because gas becomesincluded in the casting and distortion or a deformation of the producteasily occurs when annealing or otherwise heat treating the productafter casting.

In order to cast a product with a higher strength and a higher quality,specifically, it is desired to reduce the pressure in the cavity toseveral tens of Torr.

Further, from the viewpoint of improving the productivity of a diecasting machine, it is required to shorten the time required forevacuation by the vacuum pump as far as possible.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a die casting machineusing vacuum casting capable of achieving a higher vacuum in the cavity.

According to a first aspect of the present invention, there is provideda die casting machine comprising a movable die and a fixed die, a vacuumpump for reducing pressure in a cavity formed between the dies, and aninjection apparatus for injecting and filing molten metal into thecavity at a reduced pressure, at least one of the dies including anevacuation path connected with the vacuum pump and communicated with thecavity, a valve element for opening and shutting the evacuation path,and an electromagnetic driving means for making the valve element movelinearly in the opening and shutting direction by electromagnetic force.

In the first aspect according the present invention, since anelectromagnetic driving means is used for driving the valve element foropening and shutting the evacuation path formed in the die, it becomespossible to rapidly move the valve element.

Further, in the first aspect of the present invention, the valve elementmay be arranged between the parting faces and form a valve seat portionintegrally with a die. Due to this, it becomes possible to reliably openand shut the evacuation path.

According to a second aspect of the present invention, there is provideda die casting machine comprising a movable die and a fixed die, a vacuumpump for reducing pressure in a cavity formed between the dies, aninjection apparatus for injecting and filing molten metal into thecavity with a reduced pressure, an ejecting pin, for ejecting a productformed in the cavity, inserted into an insertion hole formed in a dieand communicated with the cavity, a sealing member for sealing betweenthe ejecting pin and the insertion hole to prevent air from flowing intothe reduced pressure cavity, and a temperature rise prevention means forpreventing a rise in the temperature of the ejecting pin due to contactwith the formed product.

In the second aspect according the present invention, the temperaturerise prevention means is provided to prevent a sealing member such as anO-ring from being damaged by heat.

Due to this, it becomes possible to keep the cavity sealed reliably bythe sealing member and prevent air from flowing in and to create a highvacuum in the cavity.

According to a third aspect of the present invention, there is provideda die casting machine comprising a movable die and a fixed die, a vacuumpump for reducing pressure in a cavity formed between the dies, and aninjection apparatus for injecting and filing molten metal into thecavity with a reduced pressure, at least one of the dies including anevacuation path connected with the vacuum pump and communicated with thecavity, a plurality of valve elements for opening and shutting theevacuation path, a plurality of electromagnetic driving means for movingthe valve elements linearly in the opening and shutting direction byelectromagnetic force, and a control means for independently controllingthe drive operations of the electromagnetic means.

In the third aspect according the present invention, by independentlycontrolling a plurality of electromagnetic means, it becomes possible toshorten the time required to create a high vacuum in the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments given with reference to the accompanying drawings, in which:

FIG. 1 is a view of an example of the configuration of a die castingmachine to which the present invention is applied;

FIG. 2 is a view of a die-opening state of the die casting machine shownin FIG. 1;

FIG. 3 is a view of the configuration around the dies according to thefirst embodiment of the present invention;

FIG. 4 is a view of the configuration of the parting face of the fixeddie;

FIG. 5 is a view of the configuration of the parting face of the movabledie;

FIG. 6 is a sectional view of the configuration around the valvemechanism 21;

FIG. 7 is a sectional view of the concrete configuration of the sealcooling mechanism 61;

FIG. 8 is a view for explaining the operational state of the valvemechanism 21;

FIG. 9 is a view for explaining the relationship between the reducedpressure and the injection speed in the cavity;

FIG. 10 is a sectional view of the configuration around the diesaccording to the second embodiment of the present invention; and

FIG. 11 is a view for explaining the relationship between the reducedpressure and the injection speed in the cavity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, preferred embodiments will be described with reference to theaccompanying drawings.

First Embodiment

FIG. 1 is a view of an example of the configuration of the die castingmachine to which the present invention is applied.

In FIG. 1, the die casting machine I is provided with a base 100, afixed die plate 91 arranged on the base 100, a fixed die 2 attached tothe fixed die plate 91, an injection apparatus 95 arranged on theopposite side of the fixed die plate 91 from the fixed die 2, a movabledie plate 3 arranged on the base 100 facing the fixed die 2, a movabledie 3 attached to the movable die plate 3 facing the fixed die 2, a linkhousing 71 connected to the fixed die plate 91 by tie bars 80 throughthe movable die plate 92, and a toggle die clamping mechanism 109consisting of a plurality of links which connects the link housing 71and the movable die plate 92.

The fixed die plate 91 is fixed on the base 100, while the movable dieplate 92 is arranged movably on the base 100.

The link housing 71 and the fixed die plate 91 are connected by aplurality of tie bars 80 which pass through the movable die plate 92.Normally, there are four tie bars.

The toggle die clamping mechanism which connects the link housing 71 andthe movable die plate 51 is provided with two pairs of link systems 110,only one of which is shown in detail in FIG. 1. FIG. 1 shows theconfiguration of one of the pairs in detail. Each of link systems isprovided with an angled first link 110-1 and a straight second link110-2. The first link 110-1 has an end pivoted to the link housing 71and another end pivoted to a cross head 105. The second link 110-2 hasan end pivoted to the first link 110-1 at a location between the pivotpoints to the link housing 71 and the cross head 105 and another endpivoted to the movable die plate.

This cross head 72 pivoted to the first link 110-1 of the toggle dieclamping mechanism 109 is moved in a direction as shown by arrows A1 andA2 along the screw shaft 106, whereby the toggle die clamping mechanism109 operates and causes the link housing 71 to be moved to or moved awayfrom the movable die plate 92.

The screw shaft 73 is driven by a not illustrated servo motor arrangedat the link housing 71. By the rotation of the screw shaft 73, the crosshead 72 engaged with the screw shaft 73 is moved in,the direction asshown by the arrows A1 and A2.

As shown in FIG. 1, when the cross head 72 is moved in the direction asshown by the arrow A2 by driving the not illustrated servo motor, thetoggle die clamping mechanism 109 is operated and the movable die plate92 is moved in the direction away from the link housing 71 to close thefixed die and movable die. Further movement of the cross head 72 in thedirection of the arrow A2 causes the tie bars 80 to be tensioned and thefixed die 2 and the movable die 3 to be clamped.

The injection apparatus 95 injects and fills molten metal into a notillustrated cavity formed between the clamped fixed die and movable die.By solidification of the molten metal injected into and filling thecavity, a die casting can be obtained.

On the other hand, when taking out the die casting from the dies aftercasting, as shown in FIG. 2, the cross head 72 is moved in the directionof the arrow A1. This causes the movable die plate 92 to be moved in adirection toward the link housing 71, i.e., the die opening direction,so that the movable die plate 3 is opened from the fixed die plate 2.When opening the movable die 3 from the fixed die 2, the die casting ismoved together with the movable die 3. This die casting stuck in themovable die 3 is pushed out and ejected from the movable die 3 by theejecting mechanism explained below.

FIG. 3 is a sectional view of the configuration around the diesaccording to the embodiment of the present invention. Further, FIG. 4 isa view of the configuration of a contact face (parting face) of thefixed die 2, while FIG. 5 is a view of the configuration of a contactface (parting face) of the movable die 3. Note that the fixed die 2 andthe movable die 3 shown in FIG. 3 are in a clamped state.

As shown in FIG. 3, the injection apparatus 95 is arranged at the backside of the fixed die 2.

The injection apparatus 95 is provided with a cylindrical sleeve 96arranged at the back side of the fixed die 2, a plunger tip 97 fit intothe inner circumference of this sleeve 96, a plunger rod 98 connectedwith the plunger tip 97 at its end, and an injection cylinder apparatus99 connected with the other end of the plunger rod 98.

The sleeve 96 is provided with a supply port 96 a. Molten metal ML issupplied into the sleeve 96 through this supply port 96 a by a ladle100.

The injection cylinder apparatus 99 incorporates a piston. A piston rod99 a connected with this piston and the plunger rod 98 are connected bya coupling 99 b. This injection cylinder apparatus 99 is driven byhydraulic pressure to extend and retract the piston rod 99 a.

The plunger tip 97 is connected to the plunger rod 98 and is moved inthe sleeve 96 by a drive operation of the injection cylinder apparatus99. The movement of the plunger tip 97 in the sleeve 96 supplied withthe molten metal ML toward the side of the fixed die 2 causes the moltenmetal to be filled in the cavity throughout a runner portion Rn formedby the fixed die 2 and the movable die 3.

Note that a sensor 98 a detects the number of magnetic poles N and S,formed on the periphery of the plunger rod 98 at a predetermined pitchin an axial direction, which are passed as a pulse signal. The injectionspeed of the plunger tip 97 is detected based on the number of pulses ofthis pulse signal.

The output of the sensor 98 a is supplied to a machine controller 52. Acurrent position counter 52 a in the machine controller 52 detects theposition of the plunger tip 97 based on a pulse signal from the sensor98 a.

Further, reference numeral 52 b shows a register for setting a positionwhere the plunger tip 97 passes a molten metal supply port of the sleeve96, while reference numeral 52 c shows a register for setting a positionto change the injection speed of the plunger tip 97 to a higherinjection speed. When the value of the counter 52 a reaches the value ofeither of the registers 52 b and 52 c, the machine controller 52 issuesa valve controller 51 a command to open or shut the valve of acorresponding hydraulic system for driving the plunger tip 97.

The runner portion Rn is formed from channels Rna formed on the partingface 3 a of the movable die 3 shown in FIG. 5 and the parting face 2 aof the fixed die 2.

The cavity C is formed from a curved surface Ca formed in the partingface 2 a of the fixed die 2 shown in FIG. 4 and a curved surface Cbformed in the parting face 3 a of the movable die 3 shown in FIG. 5corresponding to the shape of die casting.

As shown in FIG. 3, an evacuation path Ep is formed above the cavity C.This evacuation path is formed from a channel Epa communicated with thecurved surface Cb formed in the parting face 3 a of the movable die 3shown in FIG. 5 and a channel Epb formed in the face 2 a of the fixeddie 2 shown in FIG. 4. Note that a recess Sa adjoining the channel Epbis a contact portion of a valve described below.

As shown in FIG. 3, a valve mechanism 21 is arranged so as to becommunicated with the evacuation path Ep formed between the parting face2 a of the fixed die and the parting face 3 a of the movable die 3.

An explanation will be made of the configuration around this valvemechanism 21 with reference to FIG. 6.

As shown in FIG. 6, the valve mechanism 21 is provided with anelectromagnetic actuator 22, a valve shaft connected to theelectromagnetic actuator 22, and a disc-shaped valve element 24 formedintegrally at the front end of the valve shaft 23.

The valve shaft 23 and the valve element 24 are made of a metal materialsuch as stainless steel.

The electromagnetic actuator 22 is fixed on an opening end 29 b of acup-shaped guide member 29 via a flange member 32. The cup-shaped guidemember is inserted and tightly fit into an insertion hole 3 h formed inthe movable die 3.

An O-ring made of a plastic is interposed between the guide member 29and the insertion hole 3 h formed in the movable die 3 to seal them.

A guide hole 29 a is formed at the bottom portion of the guide member29. The valve shaft 23 is movably inserted and tightly fit into thisguide hole 29 a. From the viewpoint of the stability at the time ofmovement, the portion which fits in the guide hole 29 a is made largerin diameter than the valve element 24 side. Further, the valve shaft isprecisely fit with the guide hole 29 a, so the space between the guidehole 29 a and the valve shaft 23 is sealed.

The valve shaft 23 has a hollow portion 23 a inside. This is to make thespeed of movement of the valve shaft 23 higher by lightening the weightand reducing the inertia of the valve shaft 23.

In the movable die 3, an evacuation path 26 communicated with the aboveevacuation path Ep and for insertion of the valve shaft 23 is formed ina direction vertical to the parting face 3 a of the movable die 3. Notethat the portion of the movable die 3 where the evacuation path 26 isformed is formed by a different metal member 3 d for assembly of thevalve mechanism 21 in the movable die 3.

A valve seat portion 39 is formed at the front end of the evacuationpath at the parting face 3 a side. This valve seat portion 39 faces thevalve element 24 and shuts the evacuation path 26 by contact of thevalve element 24 with a valve seat 39 a formed on it. Note that thevalve seat 39 a is formed along the parting face 3 a of the movable die3.

This valve seat portion 39 is made of a material which is softer thanthat of the valve element 24. Specifically, the material is a metal suchas a copper alloy.

An evacuation path 25 is formed in the movable die 3 along a directioncrossing the evacuation path 26 at right angles. The evacuation path 25is communicated with the evacuation path 26. An attachment hole 3 g isformed above this evacuation path 25. An evacuation pipe 55 is insertedin this attachment hole 3 g.

The evacuation pipe 55 is formed with a thread on the outercircumference at the front end. This thread engages with a thread formedat the inner circumference of the attachment hole 3 g.

Further, a ring member 59 is fixed around the top end side of theattachment hole 3 g via O-rings 59 a and 59 b made of plastic to sealthe space between the evacuation pipe 55 and the attachment hole 3 g.

The electromagnetic actuator 22 has a shaft member 22 a connected withthe valve shaft 23, a not illustrated permanent magnet fixed to thisshaft member 22 a, and a not illustrated electromagnet arranged aroundthis permanent magnet inside of its case.

By supplying the electromagnet with electric power from the outside, anattraction force occurs between the permanent magnet and theelectromagnet so that the shaft member 22 a is moved linearly.

The electromagnetic actuator 22 drives the valve element 24 in adirection to open or shut the evacuation path 26 as shown by arrows C1and C2 in FIG. 6 by suitably changing the direction of the currentsupplied to the electromagnet.

As shown in FIG. 3, this electromagnetic actuator 22 is electricallyconnected to the valve controller 51 and is supplied with electric powerfrom the valve controller 51.

The valve controller 51 controls the drive operation of theelectromagnetic actuator 22 to open or shut the valve element 24. Thisvalve controller 51 is electrically connected to the machine controller52 generally controlling the die casting machine 1 and controls theelectromagnetic actuator 22 in response to a signal input from themachine controller 52.

As shown in FIG. 3, the above evacuation pipe 55 is connected to avacuum pump 50. This vacuum pump 50 evacuates air in the cavity throughthe evacuation pipe 55, the evacuation path 25, the evacuation path 26,and the evacuation path Ep. As the vacuum pump, one which can evacuatethe cavity to create a high vacuum of several to several tens of Torr isused.

The parting face 3 a of the movable die 3 is formed with a channel 3 bin which a sealing member 35 is laid. Part of the sealing member 35sticks out from the parting face 3 a. When the parting face 3 a of themovable die 3 contacts the parting face 2 a of the fixed die 2, thesticking out portion of the sealing member 35 contacts the parting faceand seals between the parting face 2 a and the parting face 3 a.

Preferably, the sealing member 35 is made of a relatively high heatresistant material such as silicone rubber. Note that a configurationwhere the sealing member 35 is laid in the parting face 2 a can also beemployed.

As shown in FIG. 5, the sealing member 35 is arranged continuously atthe periphery of the parting face 3 a of the movable die 3 withoutbreak.

Further, the evacuation path Ep, the cavity C, and the runner portion Rnare arranged inside from the sealing member 35 and are sufficiently awayfrom the sealing member 35.

Next, an explanation will be made of a specific configuration of theejecting mechanism 41.

As shown in FIG. 3, the ejecting mechanism 41 is arranged at the backside of the movable die 3.

The ejecting mechanism 41 is provided with a plurality of ejecting pins42, holding plates 43, 44 for holding ends of the ejecting pins 42, amovable plate 45 to which the holding plates 43, 44 are fixed, a guideshaft 46 for movably guiding the movable plate 45 to the movable die 3,and a seal cooling mechanism 61.

The ejecting pins 42 are formed by metal members of stainless steel etc.and are inserted and tightly fit into insertion holes 46 formed in themovable die 3. Note that, as below described, the insertion holestightly fit with the ejecting pins 42 at only the parts near the partingface 3 a of the movable die 3 and are enlarged in diameter at the otherparts to allow the pins to easily slide.

As shown in FIG. 5, the insertion holes 3 k open at the parting face 3 aof the movable die 3. The insertion holes 3 k are arranged facing therunner portion Rn, periphery of the cavity, or evacuation path Ep. Byextension of the front ends of the ejecting pins 42 from these insertionholes 3 k, the die casting stuck in the movable die 3 can be ejected.

The holding plates 43 and 44 grip the enlarged diameter rear ends of theejecting pins 42. These holding plates 43 and 44 are fixed on themovable plate 45.

As shown in FIG. 3, the movable plate 45 is movably guided in thedirection of the arrows E1 and E2. This movable plate 45 is moved by anot illustrated driving means in the direction of the arrows E1 and E2within a predetermined range. By the movement of the movable plate 45 inthe direction of the arrows E1 and E2, the front ends of the ejectingpins 42 protrude from the parting face 3 a of the movable die 3.

The ejecting pins 42 tightly fit with the insertion holes 3 k, so thereis no possibility that the molten metal will invade a space between theejecting pins 42 and the insertion holes 3 k, but there is possibilitythat air will enter between the ejecting pins 42 and the insertion holes3 k. If air can enter between the ejecting pins 42 and the insertionholes 3 k, it will be impossible to make the cavity a high vacuum whenreducing the pressure in the cavity.

Further, because the ejecting pins 42 directly contact the hightemperature die casting, there is possibility that the temperature ofthe ejecting pins 42 will also become high. Therefore, when sealing thespaces between the ejecting pins 42 and the insertion holes 3 k withsealing members (O-rings) made of plastic, there is a possibility thatthe O-rings will not be able to endure the high temperature andtherefore continuous use of the O-rings will become impossible.

In the present embodiment, in order to solve the above problem, a sealcooling mechanism is arranged at the back side of the movable die 3.

FIG. 7 is a view of a concrete configuration of the seal coolingmechanism 61.

As shown in FIG. 7, the seal cooling mechanism 61 has a plate-shapedfirst member 63 having a recess 63 h, a plate-shaped second member 64fixed to the first member 63 at the recess 63 h side, and a seal holdingmember 65 (only one shown) fixed to the first member 63 and the secondmember 64. Note that here, while only one seal holding member 65 isshown and the explanation is given of only one such member, in practicethere are a plurality of members corresponding to the number of ejectingpins.

The first member 63 is fixed to the second member to form a coolantstorage space Sa comprised of the recess 63 h of the first member 63 andthe opposing face of the second member 64. Between the first member 63and the second member 64 is interposed an O-ring 75 made of plastic toseal the first member 63 and the second member 64.

The second member 64 is fixed to the back face of the movable die 3. Aplastic O-ring 74 is interposed at the periphery between the secondmember 64 and the back face of the movable die 3 to seal the secondmember 64 and the back face of the movable die 3.

A recess 64 a is formed in the surface of the second member 64 facingthe movable die 3 positioned at the inside of the O-ring 74. A space Sis formed between the movable die 3 and the second member 64.

A supply port 63 b for supplying the coolant storage space Sa with acoolant W and an outlet 63 c for discharging the coolant W are formed inthe peripheral wall of the first member 63.

The seal holding member 65 is formed of a cylindrical member and has anenlarged diameter at the end at the back side of the movable die 3.Further, the seal holding member 65 is inserted and tightly fit at itsouter circumference into an insertion hole 63 a formed in the firstmember 63 and an insertion hole 64 b formed in the second member 64 soas to be fixed to the first member 63 and the second member 64. O-rings72 and 73 made. of plastic are held at the inner circumferences of theinsertion hole of the first member 63 and the insertion hole 64 b of thesecond member 64.

These O-rings 72 and 73 seal the outer circumference of the seal holdingmember 65 and the insertion hole 63 a and the outer circumference of theseal holding member 65 and the insertion hole 64 b.

The seal holding member 65 is provided with a through hole 65 a in thecenter into which an ejecting pin 42 is inserted and tightly fit. AnO-ring made of plastic is held at the inner circumference of thisthrough hole 65 a at the second member 64 side, while an O-ring 71 madeof plastic is held at the inner circumference at the first member 63side.

The O-rings 70, 71 seal the ejecting pin 42 and the through hole 65 a.

Further, the seal holding member 65 is provided with a hollow portion 65c and a through hole 65 b formed in the direction crossing the ejectingpin 42 at right angles.

In the above seal cooling mechanism 61, the supply port 63 b of thefirst member 63 is connected with a coolant supplying pipe 30. A coolantW is supplied to the seal cooling mechanism 61 through the coolantsupplying pipe 30. As the coolant W, water for example can be used.

The coolant supplied from the coolant supplying pipe 30 is introducedinto the coolant storage space Sa. Part of the coolant W is supplied tothe hollow portion 65 b through the through hole 65 b of the sealholding member 65.

The coolant supplied to the hollow portion 65 b cools the part of theejecting pin 42 exposed at the hollow portion 65 c.

Accordingly, the ejecting pin 42 in the vicinity of the hollow portion65 c is partially cooled. By continuously supplying the coolant W fromthe coolant supplying pipe 30, fresh coolant is circulated around thehollow portion 65 c and discharged to the outlet 63 c through thethrough hole 65 b.

On the other hand, out of the O-ring 70 and O-ring 71 which tightly fitwith the outer circumference of the ejecting pin 42, the O-ring 70functions to prevent air from entering from outside to between theinsertion hole 3 k formed in the movable die 3 and the ejecting pin 42and to prevent the coolant W from entering into the insertion hole 3 k.The O-ring 71 functions to prevent the coolant from leaking outside fromthe coolant storage space Sa.

If these O-rings 70 and 71 were formed of a heat resistant material suchas silicone rubber or a fluororubber, the O-rings 70 and 71 would not beable to endure continuous use under an environment where the ejectingpin 42 reaches a high temperature such as over 200° C.

In this embodiment, therefore, even if the temperature of the ejectingpin 42 rises by contact of the ejecting pin 42 with a high temperaturedie casting, because a hollow portion 65 c is arranged around theO-rings 70, 71, the temperature of the part of the ejecting pin 42contacting the O-rings 70 and 71 is kept below 100□ C. As a result, theO-rings 70 and 71 are not damaged by heat.

Next, an explanation will be made of an example of the operation of theabove die casting machine 1.

First, from the state of the die casting machine 1 shown in FIG. 2, thatis, from the state where the movable die 3 is opened from the fixed die2, the machine controller 52 operates the toggle die clamping mechanism110 to clamp the fixed die 2 and the movable die 3.

By clamping the fixed die 2 and the movable die 3, the sealing member 35seals the parting face 2 a of the fixed die 2 and the parting face 3 aof the movable die 3.

At the time of startup of the die casting machine 1, the above sealcooling mechanism 61 is already supplied with the coolant W.

Further, at the time of startup of the die casting machine 1, the vacuumpump is also started, but the valve element 24 of the valve mechanism 21shuts the evacuation path 26. Therefore, the cavity is not evacuated.

On the other hand, the sleeve 96 of the injection apparatus 95 issupplied with a predetermined amount of molten metal such as aluminumalloy by the ladle 100.

When the ladle 100 finishes supplying the molten metal, the plunger tip97 is driven under the control of the machine controller 52. When thefront end of the plunger tip 97 passes the supply port 96 a of thesleeve 96, the sleeve is sealed by the plunger tip 97 to cut off entryof air to the cavity C from the sleeve 96 side.

Note that the plunger tip 97 is driven normally at a low speed whenstarting to move the plunger tip 97.

The machine controller 52 judges when the plunger tip 97 has passed thesupply port 96 a of the sleeve 96 and outputs a command to open thevalve element 24 of the valve mechanism 21 to the valve controller 51.

Receiving the command from the machine controller 52, the valvecontroller 51 supply electric power for driving the electromagneticactuator 22 of the valve mechanism 21 to the electromagnetic actuator.

When the electromagnetic actuator 21 is driven, as shown in FIG. 8, thevalve element 24 is moved in the direction of the arrow C2, contacts acontact face Sa formed at the parting face 2 a of the fixed die 2, andstops.

At this time, because the valve element 24 is driven by theelectromagnetic actuator 22, it takes a substantially constant time ofmore than several ms or less than 20 ms to open the valve element 24.For example, in case of using a hydraulic cylinder to drive the valveelement 24, it takes 200 some odd milliseconds until the valve element24 is completely opened. Further, this time is uneven.

By this movement of the valve element 24, a space is formed between thevalve element 24 and the valve seat 39 a. Air (gas) in the cavity isevacuated from this space between the valve element 24 and the valveseat 39 a through the evacuation path Ep communicated with the cavity C,the evacuation path 26, the evacuation path 25, and the evacuation pipe55.

The sealing member 35 seals reliably the parting face 2 a of the fixeddie 2 and the parting face 3 a of the movable die 3. Further, becausethe O-rings 70 arranged at the seal cooling mechanism 61 reliably sealthe ejecting pins 42 and the movable die 3, the pressure in the cavityis rapidly reduced.

Here, an explanation will be made of the relation between the pressurereduction in the cavity and the injection speed with reference to thegraph shown in FIG. 9.

The curve (1) shown in FIG. 9 shows the pressure reduction in thecavity. The curve (2) shows the injection speed of the plunger tip 97.Note that the curve (3) shows a comparative example of pressurereduction in a cavity when operating a valve using a conventionalsolenoid valve and hydraulic or air cylinder apparatus. The curve (4)shows the pressure reduction in the cavity when closing an evacuationpath by driving a valve with inertia of molten metal injected and filledin the cavity. The curves (3) and (4) show the pressure reduction in adie casting machine not provided with the seal cooling mechanism 61 andthe continuous sealing member between the parting face 2 a of the fixeddie 2 and the parting face 3 a.

As shown by the curve (1), if the time of start of pressure reduction ispt1, because of the good response of the valve element 24, the pressurein the cavity is rapidly reduced from the pressure reduction start timept1. Further, because there is almost no leakage of air between theejecting pins and the die or between the parting face 2 a of the fixeddie 2 and the parting face 3 a of the movable die 3, it is understoodthat the pressure in the cavity is efficiently reduced in a short time.

On the other hand, in the curve (3) or the curve (4), because of using acylinder apparatus to drive the valve, the time lag from the pressurereduction start time pt1 until the pressure reduction actually starts isrelatively long and there is leakage of air from between the ejectingpins and the die or between the parting face 2 a of the fixed die 2 andthe parting face 3 a of the movable die 3. Therefore, the pressure inthe cavity is not efficiently reduced.

Along with movement of the plunger tip 97, the runner portion Rncommunicating with the cavity C and the sleeve 96 is also filled withthe molten metal ML. In this state, the cavity becomes a high vacuum ofabout 20 to 40 Torr.

The molten metal is injected into and fills the cavity by changing theinjection speed of the plunger tip 97 to a high speed. That is, theinjection speed is changed to a high speed at the high speed injectionstart time pt2.

However, it is necessary to shut the evacuation path by the valveelement 24 to prevent the molten metal ML from intruding into the valvemechanism 21 before changing to high speed injection.

Preferably, the timing for shutting the evacuation path 26 by the valveelement 24 is immediately before the high speed injection start timept2. That is, this is because there is possibility that after shuttingthe evacuation path 26 by the valve element 24, the cavity C will not beevacuated and the pressure in the cavity will rise due to leakage ofair.

In the present embodiment, however, because of using the electromagneticactuator 22 for driving the valve element 24 and making the valve shaft23 light in weight, it is possible to shut the evacuation path 26 in ashort time of as much as several ms to less than 20 ms. Further, becausethere is almost no unevenness of the response of the electromagneticactuator 22, it becomes possible to inject the molten metal into thecavity immediately before the high speed injection start time pt2.

Note that the timing for shutting the evacuation path 26 by the valveelement 24 is determined by the machine controller 52 based on thedetected position of the plunger tip 97 and the detected pressure in thecavity. The machine controller 52 outputs a command to the valvecontroller 51 in response to these position signal and pressure signal.

When driving the electromagnetic actuator 22 and shutting the evacuationpath 26 by the valve element 24, there is possibility that the valveelement 24 will rebound and jump up because it strikes the valve seat 39a of the valve seat portion 39 at a high speed.

However, in the present embodiment, it is possible to suppress the jumpof the valve element 24 when the valve element 24 strikes the valve seatportion 39, because of use of a material suppressing rebound to form thevalve seat portion 39, that is, a softer material than the valve element24. As a result, it is possible to prevent the molten metal fromintruding into the valve mechanism 21 by mistake.

When changing to the high speed injection at the high speed injectionstart time pt2, the molten metal ML is filled in the cavity C and thensolidified. Due to this, a desirable die casting can be obtained.

In order to eject the formed die casting from the fixed die 2 and themovable die 3 clamped together, the toggle die clamping mechanism isoperated to open the movable die 3 from the fixed die.

When the movable die 3 is opened from the fixed die 2 (at this time, theplunger tip is pushing a biscuit following the runner portion Rn), theformed die casting is separated from the fixed die 2.

By operating the ejecting mechanism 41 in this state to extend theejecting pins 42 from the parting face 3 a of the movable die 3, itbecomes possible to eject the die casting from the movable die 3.

At this time, because the ejecting pins 42 directly touch the hightemperature die casting, the temperature of the ejecting pins 42 alsorises.

The seal cooling mechanism 61 partially cools the ejecting pins 42, sothe O-rings 70 and 71 are not exposed to a high temperature and thefunction of the O-rings 70 and 71 is not damaged by heat.

Further, the seal cooling mechanism 61 is continuously supplied with thecoolant W, so the temperature of the seal cooling mechanism 61 fallssufficiently compared with the temperature of the movable die 3.

Due to this, if the seal cooling mechanism 61 were to directly contactthe movable die 3, the temperature distribution of the movable die 3might be influenced and the quality of the die casting might fall. Inthe present embodiment, however, because a space is formed between theseal cooling mechanism 61 and the movable die 3, the seal coolingmechanism 61 does not directly contact to the movable die 3 and itbecomes possible to keep the seal cooling mechanism 61 from affectingthe movable die 3.

As described above, according to the present embodiment, by using theelectromagnetic actuator 22 to drive the valve element for opening andshutting the evacuation path communicating the cavity C and the vacuumpump, it becomes possible to rapidly open and shut the evacuation path.Because the electromagnetic actuator 22 is driven by electric power, itis not necessary to supply an operating fluid and it becomes possible tomake the valve mechanism 21 compact. Due to this, the freedom ofarrangement of the valve mechanism 21 with respect to the dies increasesso that it becomes easy to optimize the arrangement of the valve elementand the evacuation path communicating between the cavity C and thevacuum pump.

Because the arrangement of the evacuation path communicating the cavityC with the vacuum pump 50 can be optimized, it becomes possible tointerpose the sealing member 35 between the peripheries of the partingface 2 a of the fixed die 2 and the parting face 3 a of the movable die3 without break, secure fully the distance between the evacuation pathcommunicating the cavity C with the vacuum pump 50 and the sealingmember 35, and prevent the sealing members from being damaged by heat.

Further, according to the present embodiment, by partially force-coolingthe ejecting pins liable to rise to a high temperature, general usesealing members such as O-rings can be easily used to seal between theejecting pins 42 and the die.

Second Embodiment

FIG. 10 is a sectional view of the configuration around the dies of asecond embodiment of a die casting machine according to the presentinvention. In FIG. 10, the same reference numerals are used for the sameparts of the above described embodiment.

As shown in FIG. 10, a plurality of valve mechanism 201 and 202 arearranged at the movable die of the die casting machine.

The configuration of the valve mechanisms 201 and 202 is the same asthat of the above valve mechanism 21.

The valve mechanisms 201 and 202 are arranged in the middle of theevacuation path Ep formed between the parting face 3 a of the movabledie 3 and the parting face 2 a of the fixed die 2. The evacuation pathis communicated with the cavity C.

The evacuation path Ep is communicated with a vacuum pump 501 viaevacuation paths 301 and 302 formed corresponding to the valve mechanism201 and is communicated with a vacuum pump 502 via evacuation paths 303and 304 formed corresponding with the valve mechanism 202 in the movabledie 3.

The vacuum pump 501 is provided with an evacuation ability equal to thatof the vacuum pump 502.

The electromagnetic actuators 22 of the valve mechanisms 201 and 202 areconnected commonly with the valve controller 51.

This valve controller 51 can drive the valve mechanisms 201 and 202independently.

As described above in the first embodiment, by using the electromagneticactuator 22 to drive a valve element 24, it becomes possible to make thevalve mechanism more compact and increase the freedom of the arrangementwith respect to the die.

Due to this, it is possible to easily arrange the valve mechanisms withrespect to the die.

As mentioned above, by arranging the plurality of valve mechanisms 201and 202 at the die, it becomes possible to enlarge the total sectionalarea of the evacuation path for evacuation compared with the case ofarranging a single valve mechanism with respect to the die. Therefore,it becomes possible to efficiently evacuate the cavity C. That is, whenarranging a single valve mechanism at the die, even if the evacuationability of the vacuum pump is enhanced, it is not possible to rapidlyreduce the pressure in a short time because the sectional area of theevacuation path is small. By arranging a plurality of valve mechanisms201 and 202 at the die and enabling the valve mechanisms 201 and 202 tobe independently driven, it becomes possible to optimize the opening andshutting timings of the valves in accordance with the arrangement of thevalve mechanisms.

Next, an example will be made of the pressure reduction operation in thecavity C in the case of using the plurality of valve mechanism withreference to FIG. 11.

In FIG. 11, the curve (1) shows the pressure reduction in the cavity,while the curve (2) shows the injection speed of the plunger tip 97.

First, the movement of the plunger tip 97 is started at a low speed fromthe state with the evacuation path shut by the valve mechanisms 201 and202.

Next, at the injection start time Pt1, the valve mechanism 201 is openedand the pressure in the cavity C starts to be reduced. Note that theother valve mechanism 202 is shut in this state.

By opening the valve mechanism 201, the pressure in the cavity C israpidly reduced by the vacuum pump 501.

Next, when reaching the time Pt2 where the pressure in the cavity isreduced to some degree, the valve mechanism 201 is shut and the valvemechanism 202 is opened. By this, the reduction of the pressure in thecavity C is continued by the vacuum pump 502. These opening and shuttingoperations of the valve mechanisms 201 and 202 are made by outputtingcommand from the machine controllers 52 to the valve controller 51.

Note that as a characteristic of a vacuum pump, it is known that theevacuation speed gradually decreases along with a reduction of thepressure. For example, when the pressure is reduced by the vacuum pump501, the evacuation speed gradually falls. Due to this, by changing thevacuum pump for reducing the pressure in the cavity C to the vacuum pump502 after the reduction of pressure by the vacuum pump 501 progresses tosome extent, it becomes possible to suppress the decrease of theevacuation speed as much as possible and shorten the time required toreduce the pressure to a desirable pressure.

By reducing the pressure in the cavity by the vacuum pump 502, thecavity reaches in a high vacuum.

In this state, as shown at the time Pt3 of the curve (2), the injectionspeed of the plunger tip 97 is changed to a high speed.

On the other hand, from the viewpoint of maintaining the cavity at ahigh vacuum, it is preferable that the timing to shut the valvemechanism 202 be as late as possible. Accordingly, even after changingto high speed injection, by leaving the valve mechanism 202 open so longas the molten metal does not reach the valve mechanism 202, it becomespossible to reliably suppress the rise of the pressure in the cavity Cafter shutting the evacuation path communicated with the vacuum pump502.

In the present embodiment, the valve mechanism 202 is shut afterchanging to high speed injection as at the time Pt4 in the curve (2).

The time required for the high speed injection is short such as forexample 40 ms to 200 ms. In the present embodiment, because of using theelectromagnetic actuator 22 in the valve mechanism, it becomes possibleto shut the valve mechanism 202 timely in such a limited time.

Further, the valve mechanism 202 is located away from the cavity Ccompared with the valve mechanism 201. By shutting the valve mechanism202 located apart like this last, it becomes possible to prevent themolten metal from entering into the valve mechanism while delaying thetiming to shut the evacuation path communicated with the cavity C asmuch as possible.

Summarizing the effects of the invention, as described above, accordingto the present invention, it is possible to provide a die castingmachine using vacuum casting which can realize a high vacuum in thecavity.

Further, according to the present invention, it becomes possible toefficiently reduce the pressure in the die cavity in short time.

While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

What is claimed is:
 1. A die casting machine comprising: a movable dieand a fixed die, a vacuum pump constructed and arranged to reducepressure in a cavity formed between the movable die and the fixed die,and an injection apparatus constructed and arranged to inject and fillmolten metal into the cavity at a reduced pressure, a first evacuationpath formed in at least one of parting faces of said movable die andsaid fixed die and communicated with the cavity, a second evacuationpath which connects said first evacuation path and said vacuum pump,said second evacuation path being formed inside one of said movable dieand said fixed die, a valve seat portion arranged at a connecting partbetween said first evacuation path and said second evacuation path andprovided with a valve seat, a valve shaft provided with a valve elementcontactable with said valve seat to open and shut between said first andsaid second evacuation path, said valve shaft having a hollow portionconfigured to reduce a weight of said valve shaft, and anelectromagnetic driving component constructed and arranged to move thevalve shaft linearly in the opening and shutting direction of the valveelement by electromagnetic force, wherein the valve seat portion is madeof a metal material that is softer than a metal material of said valveelement to suppress a jump of the valve element when the valve elementstrikes the valve seat.
 2. A die casting machine as set forth in claim1, further comprising a ring-shaped and seamless sealing member made ofsilicone rubber, wherein said ring-shaped member is arranged betweensaid parting faces and surrounding said cavity and said first evacuationpath to seal between said parting faces of said movable die.
 3. A diecasting machine as set forth in claim 1, wherein one of said partingfaces of said movable die has a groove in which said sealing member islaid.